In the state of the art agricultural tractors are equipped with an internal combustion engine that drives both the wheels for the forward propulsion of the tractor during operation and the power take-off shaft that is used for the drive of attached implements, such as ground breaking implements or rotobalers. A power take-off shaft gearbox is positioned between the engine and the power take-off shaft output shaft of the tractor. As a rule such power take-off shaft gearboxes are provided with several gear ratios that can be selected by an operator, that result in desired power take-off shaft rotational speeds at certain engine rotational speeds. The power take-off shaft gearboxes can also be brought into a neutral condition, in which the power take-off shaft can be rotated freely.
In known embodiments, the power take-off shaft gearboxes are shifted mechanically. A shift lever is located at the operator's station of the tractor and is connected at all times with the power take-off shaft gearbox by means of transmission elements, such as, linkages or rope pull or push-pull cable controls. In other power take-off shaft gearboxes the shift lever is located directly at the power take-off shaft gearbox housing, such that the operator must leave the operator's station and move to the rear of the tractor where the power take-off shaft gearbox is located in order to shift the power take-off shaft gear box.
In another example, an input assembly with several keys is arranged at the operator's station and each of the keys is used to select a gear ratio or the neutral position of an electro-hydraulically controlled power take-off shaft gearbox.
In these examples, only a single input assembly is provided with which the operator can select the gear ratio of the power take-off shaft gearbox.
In another prior art tractor, the drive of the power take-off shaft can be turned on and off by a switch located in the operator's cab. A second switch for the control of the drive of the power take-off shaft is located at the rear of the tractor above the fender. Still another example includes an outside key that makes it possible to operate control implements, such as the power take-off shaft from the outside of the operator's cab.
Therefore, there is a need for a shift assembly for the selection, by the operator, of gear ratio of a power take-off shaft gearbox that allows the operator to select a gear ratio for the power shaft take-off shaft gearbox or the neutral position without leaving the operator's station.